Non-Marine Mass Extinctions

Non-marine animals (amphibians, reptiles, birds and mammals) have apparently experienced at least 10 distinct episodes of intensified extinctions over the past 300 million years. Eight of these extinction events are concurrent with known marine mass extinctions, which previously yielded evidence for an underlying period of 26.4 to 27.3 million years ago. In new research, a team of scientists from New York University and Carnegie Institution for Science performed an analysis of the ten recognized non-marine mass extinctions and detected a statistically significant underlying periodicity of 27.5 million years; they also found that these mass extinctions align with major asteroid impacts and devastating volcanic outpourings of lava called flood-basalt eruptions.

Ankylosaurus magniventris, a large armored dinosaur species, witnesses the impact of an asteroid, falling on the Yucatan peninsula 66 million years ago. Image credit: Fabio Manucci.

“It seems that large-body impacts and the pulses of internal Earth activity that create flood-basalt volcanism may be marching to the same 27-million-year drumbeat as the extinctions, perhaps paced by our orbit in the Milky Way Galaxy,” said lead author Professor Michael Rampino, a researcher in the Department of Biology at New York University.

About 66 million years ago, 70% of all species on land and in the seas, including the non-avian dinosaurs, suddenly went extinct, in the disastrous aftermath of the collision of a large asteroid or comet with the Earth.

Subsequently, paleontologists discovered that such mass extinctions of marine life, in which up to 90% of species disappeared, were not random events, but seemed to come in a 26.4-27.3 -million-year cycle.

In their new study, Professor Rampino and colleagues examined the record of mass extinctions of land-dwelling animals and concluded that they coincided with the extinctions of ocean life.

They also performed new statistical analyses of the extinctions of land species and demonstrated that those events followed a similar cycle of about 27.5 million years.

What could be causing the periodic mass extinctions on land and in the seas?

Mass extinctions are not the only events occurring in cycles: the ages of impact craters — created by asteroids and comets crashing to the Earth’s surface — also follow a cycle aligning with the extinction cycle.

Astrophysicists hypothesize that periodic comet showers occur in the Solar System every 26 to 30 million years, producing cyclical impacts and resulting in periodic mass extinctions.

The Sun and planets cycle through the crowded mid-plane of the Milky Way about every 30 million years.

During those times, comet showers are possible, leading to large impacts on the Earth.

The impacts can create conditions that would stress and potentially kill off land and marine life, including widespread dark and cold, wildfires, acid rain, and ozone depletion.

“These new findings of coinciding, sudden mass extinctions on land and in the oceans, and of the common 26- to 27-million-year cycle, lend credence to the idea of periodic global catastrophic events as the triggers for the extinctions,” Professor Rampino said.

“In fact, three of the mass annihilations of species on land and in the sea are already known to have occurred at the same times as the three largest impacts of the last 250 million years, each capable of causing a global disaster and resulting mass extinctions.”

The scientists were surprised to find another possible explanation beyond asteroids for mass extinctions: flood-basalt eruptions, or giant volcanic eruptions that cover vast areas with lava.

All eight of the coinciding mass extinctions of land-dwelling and marine animals matched times of flood-basalt eruptions.

These eruptions also would have created severe conditions for life, including brief periods of intense cold, acid rain, and ozone destruction and increased radiation; longer term, eruptions could lead to lethal greenhouse heating and more acid and less oxygen in the ocean.

“The global mass extinctions were apparently caused by the largest cataclysmic impacts and massive volcanism, perhaps sometimes working in concert,” Professor Rampino said.

The research is published in the Historical Biology, an International Journal of Paleobiology.

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Michael R. Rampino et al. A 27.5-My underlying periodicity detected in extinction episodes of non-marine tetrapods. Historical Biology, published online December 10, 2020; doi: 10.1080/08912963.2020.1849178